Wireless signaling system



E. F. W. ALEX/ANDERSON WIRELESS SIGNALING SYSTEM Fiied April 19. 1916 2Sheets-Sheet 1 E. F. w. ALEXANDERSON WIRELESS S IGHALING SYSTEM FiledApril 19 1916 2 Sheets-Sheet 2 Fig.4.

lnven tor Ernst FVV. Ne nderspn,

i atented Aug. 28, R9230 entree sraras I eraser Pemeaten,

ERNST I. W. ALEXANDERSON, OF SENIEG'IADY, NEW YORK, ASSIGNOR T0 GENEELECTRIC COMPANY, A CORPORATION OF NEW YORK.

WIRELESS SIGNALING SYSTEM.

Application filed April 19, 1916. Serial No. 92,156.

To all whom it may concern:

Be it known that I, ERNST F. W. ALEX- ANDERSON, a citizen of the UnitedStates, residing at Schenectady, county of Schenectady, State of NewYork, have invented certain new and useful Improvements in WirelessSignaling Systems, of which the following is a specification. 9 Mypresent invention relates to wireless signaling systems, and moreparticularly to a system in which means is provided for over- :oming theeffect of static disturbances in the receiving instruments.

Electrostatic disturbances occur continuously in the atmosphere, sendingout electromagnetic waves of varying frequency, which will in thedescription which follows be referred to as strays. These waves areabsorbed by the receiving antenna and among the variety of wavesabsorbed there are always some which are in resonance, that is, whichhave the same length as a signal which is to be received andconsequently act upon the receiving devices in the same way as thesignal. Having analyzed this condition both mathematically andexperimentally I have come to the conclusion that F a fundamental rulemust be the basis of any device used for decreasing the effect of staticdisturbances. Any discrimination be- 1 tween a wave of the samefrequency origi nating from static and from the signal must be based onsome difi'erence in character between these two waves. If the strayswere like the signals both in frequency and amplitude variation, and inaddition to that stronger than the signals, there would be no wayconceivable for discriminating between one and the other. The longer theperiod is during which the strays and the signaling waves can becompared, the greater is the chance for finding a distin uishingdifference in the sequence of amplitude variations if in nothing else.In order that the device be effective for discrimination against.strays, it should therefore be designed so that the wave trains can bedistinguished by comparing their character for sufficiently longperiods. The receiving devices which are at present used commerciallyare constructed so as to take advantage of this law to a certain extentby using a highly resonant receiving circuit on which the signal can beallowed to act for a considerable number of successive alternations. Thereason why these devices do not entirely discriminate against strays isthe fact that the receiving antenna is set in oscillation by staticshocks and stray waves of short duration and thus I the time duringwhichthe disturbance can act upon the receiving device is prolonged toabout the same degree as the signal.

One of the objects of my invention is to provide a means for prolongingthe time during which the signal can act with accumulative effect on thereceiving device considerably beyond the time during which disturbancescan act.

In attaining this object I make use of a tuned circuit of lower thanradio frequency but above audibility, for effecting the prolongation ofthe time during which the signal and disturbance may be compared. Thedesired lower frequency is provided by means of interference'beatsbetween two radio frequencies: Both of these frequencies may be producedat the sending station, or one of them may be produced .at the receivingstation. I also provide means for roducing, transmitting and receivingth radio frequencies. An arrangement of this kind is more effective thanone employing a single radio frequency because it is more selective andproof against interference, both frequencies being nec essary to producean impression in the receiver. Also when means is rovid d at the sendingstation-for establishing the beat frequency a less delicate adjustmentof frequency is necessary than when the beat freucncy is the result ofthe difference between two high frequencies. A further object of myinvention is to provide means for em.- ciently producing signals of thedesired character. Another object of my invention is to provide suitablereceiving apparatus for ren dering audible at the receiving station thesignals sent from the transmitting station and for enabling thereceiving operator to readily distinguish between efi'ects roduced bythe static shocks and those pro need by the desired signal. Stillanother object of I The features of my invention which I believe to bepatentable are pointed out with particularity in the appended claims.The invention itself however, together with further objects andadvantages thereof, will best be understood by reference to thefollowing description taken in connection with the accompanying drawingin which Figs. 1, 2' and 3 illustrate different modifications of thecircuit connections which may be employed in transmitting signals inaccordance with my invention, and Figs. 4, 5, 6 and 7 show differentmodifications of the receiving circuits which may be employed.

In the form of transmitting system shown in Fig. 1, an alternator 1supplies current of radio frequency to the antenna 2 through thecoupling transformer 3. This alternator is designed to furnishcontinuous waves of a definite frequency and amplitude. Instead oftransmitting the signals by waves of this nature, however, I produceamplitude pulsations in the waves supplied by the alternator of such anature that the resulting wave may be resolved into two waves ofdifferent frequeneies which may be transmitted simultaneously. In orderto accomplishthis 1 divide the antenna circuit into two branches and inthese branches connect the windings of two ma netic controllers oramplifiers 4 and 5. Each of these branch circuits include half of thesecondary of transformer 3 the middle point of which is grounded. hemagnetic controllers or amplifiers which ll prefer to use in the presentcase,

' audibility.

' actions are opposite.

both as to their construction and method of operation, are described indetail in my Letters Patent of the United, States 1,328,797.

Each controller comprises a reactive winding consisting of two coils 6and 7 wound upon independent magnetic cores 8 and 9. The two coils ofeach Winding are connected in parallel with each other in the circuitand are so arranged that their magnetizing Each magnetic con troller isalso provided with two controlling windings 10 and 11 wound around themagnetic cores 8 and 9 as indicated, so that magnetization produced bythe currents in the controlling windings will be in the same directionin both cores. Controlling windings 11 are both supplied from the samesource of current, which in the present case may be an alternator 12 ofmuch lower frequency than that of alternator 1, yet having a fre uencyabove the range of ontrollifig windings 10 are supplied with directcurrent from any suitable source, such, for example, as

thedirect current generator 13 shown in.

the drawing. The controlling windings 10 are so connected to thegenerator 13 that magnetic effects upon the controllers are oppositewith respect the instantaneous magnetic reactions setup in the mea ercontrollers by current from generator 12.

The controlling windings 10 and 11 are so proportioned and the currentsources 12 and 13 so chosen and adjusted that-the maximum ampere turnsof winding 11 is approximately equal to the ampere turns of thecontrolling winding 10. As a result the controller 4: will have amaximum of controlling ampere turns when the controlling ampere turns ofcontroller 5 is practically zero and vice versa. The characteristics ofthe controllers 4 and 5 are such that the alent to an open circuit inthe connection to the other terminal. After the phase of the controllingcurrent wave supplied by alternator 12 is changed 180 electrical degreesthe other controller acts as a short circuit and the first as an opencircuit, thus reversing the .polarity of the radio frequency current ledto the antenna. At intermediate points the voltage varies between thesetwo extremes in accordance with the sine wave law. The current wave thussupplied to the antenna has an amplitude pulsation substantially inaccordance with the sine wave law and the impulses in every other groupof waves are opposite in phase to corresponding impulses in theintermediate groups of waves. The frequency of these amplitudepulsations is equal to the frequency or a multiple of the frequency ofthe alternator 12.

For 'a description in greater detail of the operation of thisarrangement reference may be had .to my nited States Patent 1,386,830.

The wave thus produced in the antenna may be resolved into two waves ofconstant amplitude, one having a frequency greater than that of thealternator l by an amount equal to the frequency of alternator 12 andtheother having a frequency as much lower than that of the alternator 1. Ifeither one of the magnetic amplifiers 4: and 5 were used alone it wouldbe possible to transmit from a single antenna waves of any one of threefrequencies, and, by providing multiple tuning of the antenna, waves oftwo'or more frequencies may be transmitted simultaneously. For example,the variable inductance let may provide for one tuning and th variablecondenser 15 in shunt to inductance 16 may provide for a second tuningat a different" requencyf' If, for example, alternator 1 has a frequencyof 'Z5,000 cyelres' and alternator 12, 5000 cyc es, the antenatal-nay betuned for 80,000v and 75,00O.cycles; 80,00()

- and 7 0,000.cycles,or 7 5;000. and70,000 cycles.

iding a third tuned circuit in mul- By prov I tiplewith the antenna-allthree frequencies fundamental frequency is suppressed and the antenna.will be tuned for the two. frequen cies into which the resultantwavejmay be resolvcdythat is, one frequency higher than that of thealternator-'1 byv an amount equal to the frequency of the alternator 1.Variable-condensers. 17

; may be connected in series with the windings 6'and 7 of thecontrollers to neutralize the.

ill

V plitude pulsations} cillating energy storage circuit may be madeleakage inductance in the windings thereof so' as to bring the minimumvalue" of the impedance as-near as possible to a short C1I cuit. It mayalso 'be' desirable to employ condensers 18 in series with each} branchof the high frequency winding of sucha value that they offer verylittleiimpedance to the flow of the high frequencycurrentfrom alternator1, but a high impedance to currents of the frequency of valternatori'l2;which may be 'inducedin the closed i i formed y the owindingsfi andz7;

is less thanit would be. if it" delivered full I power continuously. Toovercome-thisdisadvantage an oscillating circuit may pro 1 vided whichis capable of storingupconsiderably more-energy than thealt'ernator-Jmust give out during "oneiperiod of the ammay be stored up intheoscillating circuit when the energy taken by the antenna is a minimumand when the energy taken by the antenna is a 'maximurn' energy may bedrawn momentarily from the oscillating ciredit at a greater rate thanthe alternator is abler'to deliver, In the presentcase the os up of theprimary of transformer 3 and condenser 19'.

In order to transmit telegraphic signals by the system described a. key20 may be in-' serted in the circuit of alternator 12. When this key isopen the impedance of the two controllers 4 and 5 will be equal andsince they are connected in opposition to each other no current will besupplied to the antenna. When the key is closed currents havingamplitude pulsations will be supplied to the antenna in the mannerdescribed.

In Fig. 2 I have shownan organization in of the alternator 12 and theother frequency asmuchlower than that By this meansenergyployed tosecure .the desired frequency splitting. In this case a singlecontrolling windwhich a single magnetic controiier 21 is em- 1 ing 22 isshown and the alternator 12 is con- I I ling windings 6 and 7 of thiscontroller-.-arc V connected in shout to the secondary of transformer 3instead of in series as in the arrangement shown in Fig. 1. An oscillat'ing' energy storage circuit comprising inductance 24 andcondenser 25connected in' shunt to. thesecondary of transformer 3 functionsfin amanner similar to that of the energy storagecircuit described inconnec-' tion-with the arrangement of Fig. 1, Two different antennatunings may be secured by means of the variable inductance 26 anithc'variable condenser 27 and inductance 28- in: shunt'toa portionofinductance 26- In Fig. 3 Ihaveillustr tedanother modiyficationin whichthe circuit which provides :the second tuning for theiantenna is alsoutilized as an energy storage circuit. Controller 5'in this case isconnected in series with the antenna and controller 4 in a circuit inshunt to the secondary of trans- I 1 v former 3. The main antenna tuningis made 'VVith thesystem whi hhas-been'described' above, in orderv tovproducecthe amplitude' pulsations of current, the Outputdelivered bymeans of variable inductance '30 and the lse'cond tuning by variablecondenser 31 "This-condenser in connection with inductanc'es32 forms anenergy storage circuit. When controller 4 forms a short circuit if thephase relations of the currents are properly adjusted energy will bedelivered to the'storage circuit by means of transformer 33v and whencontroller 5 forms a short circuit energy will be delivered to theantenna from the alternator and the storage circuit.

. In Fig. 4 I 'haveindicated a simple form IOU of receiving outfit whichmaybe employed.

for receiving the signals transmitted by the means illustratedin Fig. 1,2 and3. In

this case the signals made up vof continuous waves having amplitudepulsations which result from the combination of the two frequenciestransmitted are received by the antenna 34 which may be aperiodic orstrongly damped, so that it will not be set into oscillation by staticshocks. The sig nals thus received are impressed upon a cirrcuit whichincludes the grid 35 of an amplifier-36 of the electron discharge typecomprisinga heated cathode 37 and cooperating anode 38 with a battery 39in the external circuit between cathode and anode. A few of the cells ofthis battery 40 may also be connected between cathode and grid in orderto adjust the grid potential to a value at which the device is mosteiiicient in amplifying the received signals. The current flowing in thecircuitl'of this amplifier which comprises electrodes 37 and 38, andbattery 39, which for conveniencein description I designate the platecircuit, will be a pulsating current. The alternating current componentof this current will flow in the secondary of transformer 41 and thecircuit 42 which comprises the secondary of this transformer, inductance43, and variable condenser 44 is tuned to the frequency of the amplitudepulsations of the waves which are to be received. The impulses actaccumulatively until the current in circuit 42 has attained its maximumamplitude. If this circuit is a highly tuned circuit the time duringwhich the current amplitude will be built up may be as much as thatcovered by 100 cycles of the amplitude pulsations; that is, if thefrequency of these pulsations is 5000 cycles it may require 1/50 of asecond for the oscillating circuit 42 to reach this maximum. If theradio frequency is 50,- 000 cycles the time for the oscillating circuit42 to reach its maximum may correspondto 1000 cycles of the radiofrequency and thus it is apparent that the energy stored in theoscillating circuit may represent the accumulated energy of 1000 Cyclesof the radio frequency. The antenna as Well as the secondary oscillatingcircuit. will also be affected by'static shocks and to a certain degreeaccumulatively. However, it can be proven by the law of probability thatthe accumulative effect of successive static shocks in any oscillatingcircuit increases by the square root of the time in which theseirregular shocks are taking place, whereas the oscillations due to thesignal, if this is a continuous wave, increase arithmetically until thecircuit has approached its maximum amplitude. WVhile it can thereforenot be expected that the secondary oscillating circuit will be free fromstatic disturbances, the relative intensity of the signal and the staticis greater the longer the time during which the energy of the signal canaccumulate. In order to make the signal audible a local source ofalternating current 45 of slightly different frequency from that of thecurrent in circuit 42 is introducedin the grid circuit of amplifier 46,so as to create beats in the receiver 47 which is inserted in the platecircuit of this amplifier and detect the-current of secondary frequencyby the well known heterodyne method. In previous attempts which havebeen made to suppress static by tuning for an audible group frequency ina spark system or its equivalent, the operator has been required todistinguish between the signal and static by the pitch of the note whichis heard in the receiving telephone. In this case although tuning isapplied to the circuit of the audible group frequency and the intensityof the currents produced by static relative to the intensity of thesignal has been decreased in somewhat the same manner as that described,there has been practically no gain by reason of this action because ofthe fact that i the currents produced by static are changed to a pitchfor'which the ear is particularly sensitive, and in fact, are changed toa pitch similar to the signal. In my system, however, in which thesecondary tuning is at an inaudible-frequency, the receiving devicediscriminates between currents of the static and the signal purely bymagnitude, and the tone pitch at which the signal is received isregulated independently by the heter'odyyne' receiver Withoiit referenceto the frequency of the discriminating oscillatory circuit.

In Fig. 5 I have shown a double tuned antenna, the branch of the antennacomprising inductance 48 and variable condenser 49 being resonant to oneof the frequencies sent out at the transmitting station and the branchwhich comprises inductance 50 and variable condenser '51 being? resonantto the other frequency which is transmitted. The two frequencies thusreceived in coils 52 and 53 will combine to produce amplitude pulsationsand these amplitude pulsations may be amplified by an amplifier such asthe amplifier 36 in Fig. 4, or may be directly impressed upon thesecondary oscillating circuit 42 of Fig. 4.

In the arrangement shown in Fig. 6 I have illustrated an additionalsafeguard against the transmission of static shocks to the receivingcircuit in which an iron core transformer is substituted for the transformer 41 of Fig. 4. This transformer is so designed that the normalstrength of a signal will work the iron at its maximum permeabilitywhereas any sudden and excessive shocks by static will saturate. theiron so that full force of the shock will notbe transmitted to thesecondary. This transformer is, in other words, a .voltage limitingtransformer which is capable of transmitting without saturation a.voltage only slightly in excessof that produced by the signals. Asindicated in the drawing the transformer in the present case com- Iprises two cores 53 and 54, each having a primary winding 55 and asecondary windmg 56. In order to regulate the saturatiou of thistransformer a third winding 57 which is common to the two cores, issupplied with a direct current from battery 58, and the value of thecurrent thus supplied may be adjusted in order to secure the desireddegree of saturation.

In Fig. 7 I have shown another modification of receiving circuit inwhich an inductance 59, which may be similar in structure to themagnetic controllers used at the transmitting station, is inserted inthe plate circuit of amplifier 36. The saturation of the iron'core ofthis inductance is adjusted by varying the current in winding 60supplied by battery 61 so that increase of current in the windings 62brings the inductance closer =to-perfect tuning for the frequency ofthe. current which results from the combination In this way it ispossible to design aresult will produce but slight increase'in.

cumulative buildin u of the two sets of waves received. This change incurrent will change the induc-- tance and this change in inductance willcause a further change in the current, this. process taking placeaccumulative'l maximum amplitude is reached. his acsembles the selfexcitation of a dynamo-electricmachine and takes an appreciable time.

cillating circuit with very high ecrement If currents produced by thepoint of maximum sensitiveness and as v the current fiowing'in thecircuit.

In the above description of receiving ap paratus it has beenassumed thatthe signals which are to be received are produced by means of twodifferent frequencies inthe, manner set forth in connection with Fig's.=1, 2 and 3; It will,however, be apparent that similar results mayobtained by ro-.

, ducinga current havin" amplitude p sasource of current differingtherefrom in he.

tions by the interaction between signals produced by a single'frequencyand a local uch an arrangement is-illustrated in Figs.

4 and 6 in which a, high frequency source of current 63 is con led tothe antenna 34 b means of a coup ing transformer 64 whic may be coupledto the coil 65 which sup-.

- plie s' the, amplifier 36, or may be connected to any suitable pointin the receiving sys-.

Y The method (if-and apparatus for trans-,- l 2,5 mitting'signals, shownin Figs. .1, 2 and 30f this application, are described and claimed inmycopending application Serial. No.

,244339, filed July 15,1918, which is a divis sion of this ap lication.I

s for receiv- The method of and apparatu ing signals, shown in F1gs.4,5,6 and 7 bf i I this application, are described and claimed l in mycopending application Serial No.

244,840, filed- July 15, 1918, which is a division of this application.A

It will of course be understood that the.

double tuned antenna may be used with the receiving circuits illustratedFig. Tas indicatedeither with .or without an ampli fier, and that manymodifications may be' made in the arrangement of the transmit- .ting andreceiving apparatus without departing from the scope of my invention asset forth in the appended claims;

What I claim as new and desirefto seruntil of the current revtection ofthis current. j

two sets of waves to interal'ct'to produce a current having amplitudepulsations of a frequency equal 'tothe difference between the cureLetters Patent of the United States, J

simultaneously receiving the waves'of dif-; 1

ferent frequencies, means for causing the two radio frequenciesbut-above audibility,

, anoscillating circuit resonant to this last frequency, and meanscooperating with the oscillating circuit for detecting the signals.

2..The combination in a wireless ,signaling-system of means ata-transmitting station for producing radio frequency currents havingdefinite amplitude pulsations of afrequency above audibility, atransmitting antenna tuned to two different frequencies,

means at a receiving station foichanging the radio frequency currentsreceived into alternating current of a frequency corresponding to theamplitude pulsations of the currents produced at the transmittingstation, and-means for the selective reception and detection of thiscurrent. 3.'-The combination in awlreless' signaling system of means ata transmitting station' for producing radio frequency currents havingdefinite amplitude pulsations of a frequency-above audibility,a'jdouble' tuned guency by an amount above audibihty;

antenna at a receiving station for receiving signals transmitted by thecurrents thus roduced at the transmitting station, means 4 or changingthe radio frequency currents received by this a'ntenna to an alternatingcurrent of a frequency corresponding to the amplitude pulsations of thecurrents pro- .duced at the transmitting station, and' means for theselectivereception and de- 4.The combination in i; eless 'signalingsystem of transmitting 'apparatus ;com-' ergy of much lower frequencybut: above audibility for controlling the flow of current --fr om theradio frequency source so that. the resultant radiation consists ofwaves of two radio frequencies differing by an amount at least as greatas the frequency of the controlling source, means at a receiving stationfor combining the currents of two radio frequencies and roducing analternating .current" of a fiequency corresponding to the frequencyof'the controlling source at the sending station, and means for.

the selective reception and detection of the current thus produced.

5. The combination in a wireless signal -ing system of transmittingapparatus comprising a source of;energy of radio freios.

no Y

"Wang 3 mm of energy -radiojfreq y, a S eCOBd controlhng sou'rcejof.en-

' double turied antenna for transmittingwaves' quency, a secondcontrolling source of ener bi ity for controlling theflowof current fromJ the, radio fr uency source so as to produce amplitude 11 sationstherein of a frequency equal to t t of the controlling source, a

' of two different radio frequencies which may be derived from thecurrent having amplitude pulsations, means at a receiving station forreceiving and combining the waves of two radio frequencies and producingan alternating current of a frequency corre- 'tion havin the receivingstation for combining the waves of two difi'erent radio frequencies tosponding to the frequency of the control ling source in the sendingstation, and:

means for the selective reception and de-* tection of the current thusproduced.

6. The combination in a wireless signaling system of transmittingapparatus comprising a source of energy of radio frequency, a secondcontrolling source of env audibility for controlling the flow of current from the radio frequency source so as to produce amplitudepulsations'therein of a fre uency corresponding to that of the controlmgsource, a double tuned antenna at a receiving station for receivingwaves of two different radio frequencies derived from the current at thetransmitting sta amplitude pulsations, means at produce an alternatingcurrent of a fre- 'ency corresponding to the frequency of e controllingsource at the sending station and means for the selective reception anddetection of the current thus produced.

7. The combination in a wireless signal 1 ing system of means at atransmitting station for producing currents of radio frequency havingamplitude pulsations'of sine wave formand'of a frequency above audi-..

bility, means for conducting this current through the antenna circuitwhich is resonant to two frequenciesdiflering from one" another by anamount above audibility in order to radiate two'sets of waves of dif-'tecting the alternating current thus pro-V duced. V

8. The method of wireless signaling which consists in transmittinsignals by means of two sets of waves 0 constant amplitude andradiofrequency difiering in frequency by an amount above audibility,receiving the waves thus transmitted and combining them to produce analternating current having a frequency corresponding to the difierofmuch lower frequency but above King a frequency corresponding quency ofthe amplitude pulsations of the current produced at the transmittingstaence in frequency of the two sets of of much lower frequency butabove audiaccumulating the energy of thi alternating? current in aresonant circuit and utiliz g the accumulated energy for the operationof sultable detecting apparatus.

9. The method of wireless signaling which consists in producingatatransmittmg'sta tion a current of radio frequency having amplitudepulsationsof a much lower frequency but above audibility, transmittingsignals by means of waves derived from the current thus "produced,receiving the trans- .mitted waves and producing from the reaccumulatedenergy for the operation of suitable detecting apparatus.

10; The method of wireless signaling which consists in produclng at atransmitting station two sets of waves of constant amplitude and radiofrequency differing in frequency by an amount above audibility,transmitting si nals by means of these waves, causing t e wavestransmltted to interact at a receiving station to produce alternatingcurrent having a frequency corresponding to the difference in frequencyof the two sets of waves transmitted accumu lating the energy of thiscurrent 1n a reso' nant circuit and causing the current in the resonantcircuit to interact with a current of difi'erent frequency to producecurrent pulsations of audible frequency.

11. The method of wireless signaling a which consists in producing at atransmitting station a current of radio frequency having am litudepulsations of much lower frequency ut above audibility, transmittingsignals by means of waves derived from the current thus produced,receivin fi -,1)v

transmitted waves and producing from the received waves an alternatingcurrent havtion, accumulating the energy of this current in a resonantcircuit and causing the current in the resonant circuit to interact witha current of different frequency to'produce'current pulsations ofaudible frequency.

12, The method of wireless signaling which consists in producing at atransmitting station a current of radio frequency having definiteamplitude pulsations of a frequency above audibility, transmittingsignals by means of waves derived from the current thus produced,receiving the waves thus transmitted in a multiple circuit tuned to twodifferent frequencies, producing by means of the waves thus received analternating current-0f a frequency. corresponding 3o lectively receivingand detecting the. alter- Q CGiVlDQi Ii';

biningthem to roduce an alternating curequency corresponding to to theamplitude pulsations of the current produced atf'the transmittingstationand selectively receiving andv detecting the alter- I, natingcurrent thus produced. w

The -method of-wireless signaling iwhich consists in transmittingsignals by *means of two sets of waves of constant am-' plitude andradio frequency differing in frequency/byi an amount above audibility,re-

e waves thus transmitted, com

rent having a the difference in frequency of the two sets of waves,andselectively receiving and detect ing the alternating current thusproduced.

14. The method of wireless signaling --which consists in producing at atransmitting station a current of radio frequency having amplitudepulsations of much lower 1 frequency but above audibility, conductingthis current through an antennacircuit which is resonant to twofrequencies differ ing. from one another by an amount'above raudibilityand thereby radiating waves. of 7 --two difierent frequencies, receivingthe waves thus radiated and combining them to produce an alternatingcurrent having a freuency corresponding vto the difference in requencyof. the two sets of waves, and senating currentthus-produced. I 15. Themethod of wireless signaling which consists in transmitting signals bymeans of two sets of wares of constant amy plitude and radio frequencydiffering in frequency by an amount above audibility, receiving thesewaves in .a-multiplecircuit which is resonantto the two frequencies,

combining the received'waves to produce an 49 alternating current havingafrequency corresponding to the difl'erence in frequency of .the twosets of Waves and selectively receiv-.

ing, and detecting" the alternating current thus produced. 2w

16. Themethod' of wireless signaling which consists in producingv atantransmitting station a current of radio frequency having amplitudepulsations of much lower frequency but above audibility, conducting 9this. current through an antenna circuit which is resonant to twofrequencies differing from one. another by an amount above audibilit andthereby radiating waves of two mdi erent frequencies, receiving thesations in the flow of power from a high frequency source in such a waythat the character of the signals depends upon sucham- V plitudepulsations, tuning an antenna at one station for more than one frequencyso that the continuous wave components into which the wavehaving-amplitude pulsations can be resolved are transmitted efficientlythrough "the several corresponding frequencies for which the antenna istuned, and

recombining the several components into a current havin amplitudepulsations similar to those originally produced.

18. The method of wireless signaling which consists in the use ofcontinuous wave signals having amplitude pulsations, resolving thesignal wave into its continuouswave components, passing these componentsthrough circuits at one station which are in resonance with thefrequencies into which the signal wave has been resolved, and recombinng these continuous Wave componature to that of the signal current.

19.The method of receiving wireless signals produced'by two transmittedcurrents of radio frequency differing from each other in frequency by anamount above audibility,

which consists in combining the two currents at a'rece'ivlng station toproduce an alternating current havinga frequency corresponding to thedifference in frequency of the twocurrents, accumulating the energy ofthis alternating current in a resonant circuit, and utilizing theaccumulatedenergy for the operation of suitable detecting apparatus. l

20. The method of receiving wireless sig nals produced by twotransmitted currents of radio frequency differing from each other by anamount above audibility which connents to produce another currentsimilar in I sists in combining the two currents at a receiving stationto produce an alternating. 'current having a' frequency corresponding tothe: difference in frequency of the two currents, accumulating-theenergy of this current in a resonantcircuit, and causing the current inthe resonant-circuit to interact with a current-of'difi'erent frequencyto produce current pulsationsof audible frequency. I 21."The combinationin a wireless signaling system, of means at-a receiving station forproducing by means of two continuous wave signaling currentsderived'from separate circuits at the receiving station a radiofrequency current having amplitude pulsa tions of much lower frequency,but above' audibility, means for producing therefrom, an alternatingcurrent having a frequency corresponding to the amplitude pulsations,means comprising a resonant circuit for accumulating the energy of thiscurrent, and means for causing the accumulated energy to interact withenergy from a source of different frequency to produce a current ofaudible frequency.

for producing in two separate circuits two currents of radio frequency,one of which corresponds to the frequency of the signaling current andthe other differing there 4 from 'by an amount above audibility, meansfor combining the two currents to produce an alternating currenthaving afrequency corresponding to the difference in frequency between the twocurrents, and means for selectively receiving and detecting the currentthus produced. a

23. The method of overcoming the effects of staticdisturbances in awireless signaling system, which consists in employing a sig-.

naling .current of radio frequency having amplitude pulsations of muchlower frequency, producing from the signaling current an alternatingcurrent having a frequency corresponding to the amplitude pulsations andpassing this current through a circuit containing a device for limitingthe energy passing therethrough to a predeter mined value, and thenthrough a circuit which is resonant to the frequency of the alternatingcurrent.

24. The method of overcoming the effects of static disturbances in awireless signaling system, which consists in transmitting signals bymeans of currents of two different radio frequencies, receiving andamplifying the signals thus transmitted, producing from the amplifiedsignal currents an alternating current having a frequency correspondingto the diflerence in frequency of the two radio frequency currents, andpass ng this current through a circuit containing a device for limitingthe energy passing there through to a predetermined value, and thenthrough a circuit which is resonant to the frequency of the alternatingcurrent.

25. The combination in a wireless receiving.

system of an antenna, means'for amplifying signaling currents receivedthereby, acir- 'cuit through which the amplified current will flow andan iron; core inductance included in said circuit, the core of saidinductance beng saturated? to sucha degree that the current which willflow through theinductance cannot exceed a predetermined desired value26. In a wireless receiving system, an oscillating circuit, an iron coreinductance in said circuit and means for adjusting the permeability ofsaid iron core, the iron core being normally so adjusted that the timerequired for oscillations to build up to a maximum is greater than thetime corresponding to the natural oscillations of a circuit havingcorres onding inductance and capacity.

27. he combination in a wireless signal- 'reeaeei ing system, of -areceivng antenna having two branches tuned to two radiofrequenciesdifi'ering; from. each. other by an amount 22. The combination in awireless signaling system, of means at a receiving station two radiofrequencies differing from each other by an amount above audibility,means for producing from the-waves? received thereby an alternatingcurrent having a frequency corresponding to the difference in' frequencyof the two sets of waves received,

and means for selectivelydetecting th'e'current thus produced.

29. The combination in ai wirele' s s signaling system, of means at areceiving station for simultaneously receiving signal waves of two radiofrequencies differing from eachother by an amount above audibility,means for-causing the two sets of waves to interact to produce a currenthaving amplitude-puldifference in frequency of the tw'o currentsreceived, and means in the receivin circuit whereby the energy of thecurrent t usp'ro- .dueed may be accumulated for a greater length of timethan the nauraljoscillations of the radio frequency current? afg 30; Thecombination in a wireless signaling system, of means at a receivingstation for simultaneously receiving signal Wavesof; two different radiofrequencies, Imeans-zfor' causing the two sets of waves received tointeract to roduce a current having amplitude pulsations of a frequency.equal'to the difference between the two radio frequencies,-

but above audibility, an os'cillating circuit resonant to this lastfrequency and means cooperating with the oscillating circuit fordetecting the signals.

' 31. The combination iii'a wireless "signal-' ing system, of means at areceivng station a no if for simultaneously receiving signal waves oftwo different radio frequencies, means for causing the two sets of wavesto interact to produce a current having amplitude, pu1-' sations of afrequency corresponding tothe difference between the tworadio-frequencies,

and means in the receiving circuit whereby the energy of the currentthusproduced may be accumulated for a greater len' hyof timethan thenatural: oscillations 0 frequency currents.

32. The method of receiving wireless signals produced by two currents ofradio frequency differing. from each other in fre'-'.

quency byan'amount above audibility, which the radio ernating CUT-3' x307 90 sations of a frequency corresponding-to the p the difference infrequency of the waves received and selectively detecting thealternating current thus produced. I

33. The method of receiving wireless signals produced by two currents ofradio frequency differing from each other in frequency by an amountabove audibility, which consists in utilizing an antenna tuned to thetwo fre uencies, producing by means of the waves t ereby received analternating current having a frequency correspondlng to the differencein frequency of the two sets of waves received, accumulating the energyof this current in a resonant circuit and causing the current in theresonant circuit to interc act with a current of different frequency'toproduce current pulsations of audibile freiqu y- 34. In a wirelessreceiving system, an oscillating circuit having an iron core inductanceincluded therein, said iron core inductance being so adjusted that anincrease of current accumulatively changes the inductance in thedirection required for exact tuning to a desired frequency whereby thecircuit is made so sensitive as to approach instability. Y I 35. Areceiving device for a wireless signaling system, comprising anoscillating circuit having therein an iron core inductance and means foradjusting the saturation in the iron core the saturation of said ironcore being normally adjusted so that the oscillating circuit approachesa state of instability. on account of the change in permeability of theiron with changes in the current in the circuit. 36. A receiving devicefor a wireless signaling system, comprising an oscillating cir- ,-cuithaving therein an iron core inductance T, which has, in addition to thealternatlng current winding, a winding supplied by a variable directcurrent for adjusting the saturation in the iron core the saturation ofsaid 4 iron core being normally adjusted to such a point on thesaturation curve that the oscillating circuit approaches a state of1nstability on account of the effect of the alternating current'upon thepermeability of'the iron, whereby the time required for building uposcillations to a maximum is prolonged beyond the time required for acorresponding circuit with constant inductance.

37. In electrical signaling, the method which consists in producing asignal-representing undamped current of radio frequency varying inamplitude at predetermined lower frequency above audibility,

converting the same into a current of frequency corresponding with saidpredetermined frequency, producing a current reacting with saidconverted current to produce beats, and utilizing said beats whose 7frequency is the diiference'between the fre quency of said convertedcurrent and the frequency of said third named current to reproduce thesignal.-

38. In electrical signaling, the method which consists in producing asignal-representing undamped current of radio frequency varying inamplitude at; predetermined lower frequency above audibility, convertingthe same by rectification into a current of frequency correspondingvwith said predetermined frequency, producing a current reacting withsaid rectified current to produce audible beats, and utilizing saidbeats whose frequency is the difference between the frequency of saidrectified current and the frequency of said third named current toreproduce the signal.

39. The combination with transmitting apparatus comprising means forproducing sustained high frequency energy varying in amplitude at apredetermined frequency, means for'controlling the energy to represent asignal or message, of receiving apparatus comprising means for producing,a current of frequency differing from said predetermined frequency toproduce beats, and a translating device utilizing the beats whosefrequency is the difference between said predetermined frequency and thefrequency of said current to reproduce the signal or message.

40. In electrical signaling, the method which consists in transmitting asignal-representing current of radio frequency varying in amplitude atpredetermined lower frequency, producing a current of frequency reactingwith the received current to roduce beats, and utilizing said beats wose frequency is the difference between said pre-.

determined frequency and the frequency of said slecond named current toreproduce the signa 41. In electrical signaling, the method whichconsists. in transmitting a signal-rep resenting current of radiofrequency varying in amplitude at predetermined lower frequency aboveaudibility,'-producing acur- 'rent of frequenc reacting with thereceived current to pro uce beats of audible frequency, and utilizingsaid beats whose frequency is the difference between said predeterminedfrequency and the frequency of said second named current to reproducethe signal.

In witness whereof, I have hereunto set my hand this 17th day of April,1916.

ERNST F. W. ALEXANDERSON.

